A conventional head-protecting airbag device having an airbag which is capable of arresting an occupant inside a vehicle in the event of a rollover of the vehicle is known, by way of example, from the Patent Document 1 listed below. In the head-protecting airbag device, the airbag includes a main inflatable region and a sub inflatable region that is in communication with the main inflatable region and completes inflation after the main inflatable region has completed inflation. The sub inflatable region includes a supportive inflatable region that is located at the lower end of the sub inflatable region as fully inflated and is adapted to be supported by a vehicle body member disposed below a beltline of a vehicle window.
With such a head-protecting airbag device, an occupant is arrested inside the vehicle smoothly in the event of rollover of the vehicle since the supportive inflatable portion is supported by the vehicle body member disposed below the beltline and prevents the airbag from moving out of the vehicle.
In another conventional head-protecting airbag device disclosed in the Patent Document 2, by way of example, the lower end of a sub inflatable region of an airbag is folded over an inboard side of an inboard side wall of the airbag, and then the whole airbag is folded up by rolling or the like and stored in a storage area disposed at the upper periphery of a vehicle window.